In butt welding of welding end faces of a pair of base materials together so as to join the end faces together in a state where the end faces are disposed to face each other, a molten region is formed by welding to pierce through the base materials in the thickness direction (piercing welding), and therefore the work efficiency of welding can be improved. Employment of submerged arc welding is effective for achievement of piercing welding. In butt welding for which submerged arc welding is employed, a measure to achieve quality improvement of a welding part or the like has been proposed (see Japanese Patent Application Laid-Open No. 2010-221298 and Japanese Patent Application Laid-Open No. 2007-260692, for example).
On the other hand, one of welding methods is a gas shielded arc welding method of consumable electrode type (e.g., Japanese Patent Application Laid-Open No. 2007-229775). A gas shielded arc welding method is a technique of generating an arc between a base material and a welding wire, which is fed to a welded part of the base material, and welding the base material using heat of the arc, and welding is performed while jetting inert gas to the periphery of a welding part especially in order to prevent oxidation of the base material which has become hot. In a case of a thin plate having a thickness of approximately 5 mm, a butt joint of the base material can be welded with one pass.
In a case of a thick plate having a thickness of 9 to 30 mm, however, it is impossible to weld the base material with one pass in a conventional gas shielded arc welding method. Therefore, welding of a thick plate is performed using multilayer welding in which a welding operation is performed repeatedly a plurality of times.
In multilayer welding, however, increase in man-hour for welding becomes a problem. Moreover, heat input becomes large, and deformation of the base material and embrittlement of a welding portion become problems.